/*

  * Copyright 2012 smartics, Kronseder & Reiner GmbH

  *

  * Licensed under the Apache License, Version 2.0 (the "License");

  * you may not use this file except in compliance with the License.

  * You may obtain a copy of the License at

  *

  *     http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package de.smartics.ci.config.load;

 import java.io.File;

 import java.io.FileNotFoundException;

 import java.io.InputStream;

 import java.net.URL;

 import java.net.URLClassLoader;

 import org.xml.sax.InputSource;

 /**

  * Manages locations to look for configuration files to load.

  */

 public final class LocationManager

 {

   // ********************************* Fields *********************************

   // --- constants ------------------------------------------------------------

   // --- members --------------------------------------------------------------

   /**

    * The locations to search for configuration files.

    */

   private DynamicUrlClassLoader locations;

   // ****************************** Initializer *******************************

   // ****************************** Constructors ******************************

   /**

    * Convenience constructor if no class loader should be used as a parent.

    */

   public LocationManager()

   {

     this(null);

   }

   /**

    * Default constructor.

    *

    * @param parentClassLoader the parent class loader to delegate requests to.

    *          May be <code>null</code>.

    */

   public LocationManager(final ClassLoader parentClassLoader)

   {

     locations = new DynamicUrlClassLoader(new URL[0], parentClassLoader);

   }

   // ****************************** Inner Classes *****************************

   /**

    * Implementation allows to add new locations dynamically.

    */

   private static final class DynamicUrlClassLoader extends URLClassLoader

   {

     private DynamicUrlClassLoader(final URL[] urls,

         final ClassLoader parentClassLoader)

     {

       super(urls, parentClassLoader);

     }

     private void addUrl(final URL url)

     {

       super.addURL(url);

     }

   }

   // ********************************* Methods ********************************

   // --- init -----------------------------------------------------------------

   // --- get&set --------------------------------------------------------------

   // --- business -------------------------------------------------------------

   /**

    * Adds a file location to the manager to search for configuration files.

    *

    * @param file the file location to be added. May reference a folder or a JAR

    *          file.

    * @throws NullPointerException if {@link file} is <code>null</code>.

    * @throws IllegalArgumentException if {@code file} does not provide a valid

    *           URL.

    */

   public void addLocation(final File file) throws NullPointerException,

     IllegalArgumentException

   {

     try

     {

       final URL url = file.toURI().toURL();

       addLocation(url);

     }

     catch (final Exception e)

     {

       throw new IllegalArgumentException(

           file.getAbsolutePath()

               + " is not a valid file. Cannot create a URL location.", e);

     }

   }

   /**

    * Adds an URL location to the manager to search for configuration files.

    *

    * @param url the URL location to be added. May reference a folder or a JAR

    *          file.

    */

   public void addLocation(final URL url)

   {

     locations.addUrl(url);

   }

   /**

    * Opens a stream to the given resource, if the resource can be found at any

    * location managed by this instance.

    * <p>

    * The client is responsible to close the resource.

    * </p>

    *

    * @param resource the resource to open.

    * @return the stream to the resource as an input source.

    * @throws FileNotFoundException if the resource cannot be opened.

    */

   public InputSource open(final String resource) throws FileNotFoundException

   {

     final URL url = locations.getResource(resource);

     if (url != null)

     {

       final InputStream in = locations.getResourceAsStream(resource);

       final InputSource source = new InputSource(in);

       source.setSystemId(url.toExternalForm());

       return source;

     }

     throw new FileNotFoundException("Cannot find resource '" + resource + "'.");

   }

   // --- object basics --------------------------------------------------------

 }